In order to reduce wiring resistance and manufacturing cost of LSI, it is preferable that a plug interconnection be formed of a plug material and a barrier metal material with low resistance and low cost. An example of the plug material may be copper (Cu). In addition, an example of the barrier metal material may be tungsten nitride (WN). When tungsten (W) is used as the plug material, main components of the plug material and the barrier metal material are the same metal so that the manufacturing cost is further reduced. However, when a tungsten nitride film is formed on a silicon (Si) substrate as the barrier metal material, silicon nitride is stable more than tungsten nitride. Formation of the tungsten nitride film may cause a problem that a silicon nitride film is formed in the silicon substrate so that electrical contact can not be obtained between the silicon substrate and the plug interconnection. The same problem may occur when an interconnection other than the plug interconnection, or an electrode such as a gate electrode, a floating gate, and a control gate is formed.